This invention relates in general to balloon catheters that are used in surgical procedures. In particular, this invention relates to an improved structure for such a balloon catheter having a retractable sheath that can quickly and easily adjust the length of the inflated portion of the balloon and a locking mechanism for selectively retaining the sheath in the desired position for use.
In many surgical procedures, such as but not limited to percutaneous transluminal angioplasty procedures, a catheter having a selectively inflatable portion provided thereon (commonly referred to as a balloon catheter) is used to open a blockage and/or place a stent in a blood vessel. To accomplish this, a user st select one of various sized balloons to match the blood vessel structure and the length of the treatment area. The balloon of the catheter is initially positioned at a desired zone of attention within the blood vessel. Then, the balloon of the catheter is inflated so as to expand into engagement with an inner surface of the blood vessel, thereby expanding the blockage. If desired, an expandable stent can be disposed about the balloon of the catheter such that when the balloon is inflated, the stent is expanded into engagement with the inner surface of the blood vessel. The balloon and/or the stent is often treated with medication that is delivered by contact with the surface of the blood vessel when the balloon and/or stent is deployed. In either event, the balloon is subsequently deflated after use.
It is important that the balloon be properly sized to the treatment area. If a balloon catheter is too long, the balloon may damage the surrounding tissue. If a balloon is too short, the treatment may be ineffective or require time-consuming repetition. Therefore, care facilities are forced to stock many different size balloon catheters and medical care providers must spend time carefully selecting the properly sized balloon catheter. What is needed is a variable length balloon catheter. Therefore, it would be desirable to provide an improved structure for such a balloon catheter having a retractable sheath that can quickly and easily adjust the length of the portion of the balloon to be inflated and a locking mechanism for selectively retaining said sheath in the desired position for use.
Due to internal pressure, shape, and texture, a partially exposed balloon catheter would have a natural tendency to escape the retractable sheath when inflated. This is much like how a partially protruding watermelon seed has a natural tendency to entirely escape a person's lips, due to the watermelon seed's shape and texture. Here, the same phenomenon applies to a partially exposed balloon catheter from a sheath, though the situation is further complicated by the internal pressure of the balloon. Therefore, it would be desirable to additionally provide a mechanical stop in conjunction with the device where said mechanical stop serves to prevent the balloon from entirely escaping the retractable sheath when the balloon is inflated. Further, the mechanical stop can be used to adjust the effective area of the balloon catheter by controlling the length of the balloon permitted to extend from the sheath.
Recently, medical practitioners have realized that drug coatings may be applied to the outer surface of the intravascular balloons to increase the effectiveness of medical treatment. These so called “drug coated balloons” are exposed to blood and other intravascular fluids upon being inserted into a person's vascular system. This may result in the premature activation, elution, dilution, and loss of the drug coating on the way to the treatment zone. Therefore, it would be desirable to provide a watertight seal between the balloon and the sheath such that the medicated balloon is not exposed to intravascular fluids until the balloon reaches the treatment zone.
The present invention is directed to an improved structure for a balloon catheter having a retractable sheath that can quickly and easily adjust the length of the inflated portion of the balloon and a locking mechanism for selectively retaining the sheath in the desired position for use. The balloon catheter assembly includes an inner member and an outer member that is disposed about the inner member. The outer member includes an inflatable balloon. A sheath is disposed about the outer member for movement relative to the balloon so as to selectively expose some or all of the balloon for inflation. The balloon catheter assembly includes a clamp for selectively securing the sheath at a desired position relative to the balloon. The inner member may comprise a series of indentations or protrusion that engage the clamp such that the user may selectively control the location of the retractable sheath relative to the balloon.
The assembly may further include a mechanical stop that is configured to selectively secure the balloon and prevents it from entirely escaping the sheath when the balloon is inflated. The assembly may comprise a series of graduated markers, such as radiopaque markers, that indicate the position of the balloon relative to the retractable sheath. The balloon may further comprise a strength collar, such as an annulus, located on the distal end of the retractable sheath.
Additionally, the balloon and the sheath may form a substantially watertight engagement with one another. This seal may prevent the medicated coating from being prematurely removed, eluted, or activated prior to the assembly being properly located at the treatment site. In exemplary embodiments of the present invention, the assembly may further comprise a cap that provides a substantially watertight engagement between said cap and the sheath when the balloon is in a retracted position such that the cap abuts the sheath. The balloon may further comprise a lubricious coating between the outer surface of the balloon and the inner surface of the sheath which allows the balloon to move relative to the sheath without disturbing the medicated coating.
Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.